Gas turbine combustors are typically configured with air feed, dilution and/or trim holes that project through the inner and outer walls of the combustor. These holes provide pressurized feed air to the combustor to support combustion of an internal fuel-air mixture. Other holes provide air flow that is designed to tailor the combustion spatially and temporally within the combustor to benefit emissions, performance or the temperature characteristics at the aft end of the combustor that enters a downstream turbine.
The air that comes out of one or more of the holes described above interacts with the fuel-air mixture in the combustor. This feed air usually enters the combustor with enough momentum to act like an air jet in cross-flow. An air jet in cross-flow is representative of a complex interaction and results in combustor liner distress (i.e., oxidation) local to dilution and trim holes. This occurs for several reasons. The presence of this jet disturbs the approaching flow along the walls of the liner and pressure gradients within the combustor, and promotes the formation of secondary flow or vortical structures. These secondary flows and vortical structures disrupt (and reduce) the cooling in the vicinity of the combustor liners by mixing with the cooling air and driving hot gases from the combustion process to the liner surfaces. Since this mixture is undergoing combustion, it can exceed the melting point of the combustor liner materials. In addition, the air jets provide a blockage for the approaching flow. This means that the flows need to accelerate around the dilution holes increasing the heat transfer and the strength of the local secondary flows. Moreover, the jet in cross-flow creates a wake that promotes a downwash of hot gases around the holes. The interaction with the approaching flow may not be uniform given swirl and non-homogeneous fuel-air distributions produced by the forward fuels nozzles, air swirlers, cooling air and air introduction. This can create a biased distress pattern on the combustor liner.